I have 2000 grand am gt Ive been having a water leak problem for a few weeks now everytime I start my car I have to full with water and in the midst of trips usually needs water also I noticed it getting worse since the winter months my heater would start blowing cold and usually needed water or the temp would start raising and most of time needed water but not always This morning got up to leave turned car on and it was making whistling noise went to add water and noticed water pump was froze How do I know whether it may thaw out or I need to replace it

Make sure the leak is sealed 1st, Diagnose & repair the leak. Drain the system, replace the water pump & installed premixed anti freeze (the type the car calls for) NOT STRAIGHT WATER.

Have you ever heard of K-Seal? That's the best cooling system stop-leak on planet earth! Under $20 at most auto parts stores ... which carry it, but some don't!

Where do you live. Never put straight water in a radiator even during the summer. Do you see any leaks around the water pump, radiator hoses, or in the passenger side floor inside also at the firewall where the heater hoses go into the heater.